A lot of formats from commercial vendors have become de facto standards. Probably the classic case is the older Microsoft Office .doc (Word), .xls (Excel) and .ppt (Powerpoint) standards, which many non-Microsoft products can recorgnize and process.

What's a little more interesting is that the Open Source movement has encouraged software vendors to make these standards "official". It's a good way to keep in business if you can get buy in.